1 / 11

Speeding Things Up

Speeding Things Up. Resistors and Capacitors together. Dr. Lu’s Guest Lecture. Activity. Work through today’s activity. What Have We Learned About RC Circuits?.

vernon
Download Presentation

Speeding Things Up

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Speeding Things Up Resistors and Capacitors together

  2. Dr. Lu’s Guest Lecture

  3. Activity • Work through today’s activity

  4. What Have We Learned About RC Circuits? • When you decrease the capacitance in an RC circuit (using capacitor C in place of capacitor A in the activity), what happens to the rise time? • Halving the capacitance resulted in what precise effect on the rise time? • When you increase the resistance in an RC circuit (using 4.7 MW in place of 2.2 MW), what happens to the rise time? • Slightly more than doubling the resistance resulted in what precise effect on the rise time?

  5. What Have We Learned About Rise Time? • How did the rise time compare with the decay time for the first circuit? • Is this similar to what you observed in the keyboard activity? • What were your rise times for • Capacitor A and 2.2 MW Resistor? • Capacitor C and 2.2 MW Resistor? • Capacitor C and 4.7 MW Resistor? • Compare to • t = RC = (0.10 mF)(2.2 MW) = 0.22 s • t = RC = (0.05 mF)(2.2 MW) = 0.11 s • t = RC = (0.05 mF)(4.7 MW) = 0.24 s

  6. The Relationship between Rise Time and Time Constant • Rise time Dt defined by Dt = t90 – t10 = t(V=0.90V0) – t(V=0.10V0) • Time constant t defined by V(t) = V0 (1 – e–t/t)(for charging circuit) • So, 0.90 V0 = V0 (1 – e–t90/t) ln (e–t90/t) = ln (1 – 0.90) = ln (0.10) t90 = – t ln(0.10) t10 = – t ln(0.90) Dt = t ln(0.90) – t ln(0.10) = t ln(0.90/0.10) = t ln 9

  7. Summary of RC Circuits • For discharging, VC(t) = V0e-t/t • For charging, VC(t) = V0 (1 - e-t/t) • q(t) = C VC(t) in each case • time constant t = RC = Dt/(ln 9) = Dt/2.20 • At any time in charging circuit, V0 = VC(t) + VR = VC(t) + iR • At any time in discharging circuit, 0 = VC(t) + VR = VC(t) + iR

  8. Why do we care about rise time? • Rise time limits speed of signal processing/transfer • Rise time limits speed of accessing electronic memory • Rise time means that shrinking does not always result in faster processes

  9. Interconnects and capacitance • Interconnects are “wires” (now strips of conductor) between circuit elements • Interconnects run along edges of devices, separated by an insulator • Charge carriers in interconnect attract opposite charges in device below them • Voila! A capacitor

  10. Important notes from Turton and Lu • Capacitors, resistors, and transistors are key components in modern electronic devices • Challenge to create 2-dimensional circuits (or at least have all connections in 2D), so some (Lu) are moving toward 3D devices • Shrinking devices saves $$ but poses problems like RC rise time, heat, new production methods, finite depletion regions, electromigration • NO PHYSICAL LIMITS REACHED YET

  11. More notes from Turton and Lu • Speed isn’t going to be drastically increased by shrinking components, due to RC complications • We can, however, use materials with “faster” charge carriers • Resistance due to collisions caused by imperfect crystal structure • Materials with lower resistance may work better • If fewer conduction states allowed to electron, it will be less likely to change direction

More Related